Tocopherols and sterols are useful alcohol compounds that can be found in vegetable oils. Tocopherols are used as a raw material for vitamin E synthesis, and sterols can be used as raw materials for synthesis of medicines such as cortisone and various sexual hormones. Treatment of vegetable oils with steam and vacuum produces a byproduct referred to as deodorizer distillate, or deodorizer sludge. This deodorizer distillate is rich in tocopherols and sterols, but also contains a multitude of other compounds. A typical batch of deodorizer distillate may contain free fatty acids (39%), a mixture of mono, di- and tri-glycerides (30%), sterols and fatty acid esters of sterols (14% total), tocopherols (9%), and the remainder hydrocarbons.
Numerous methods have been proposed for the recovery of tocopherols and sterols from deodorizer distillates and related mixtures. For example, U.S. Pat. No. 2,432,181 teaches that tocopherols can be recovered from vegetable oils and fats by reacting the fatty acid glycerides with an aliphatic monohydric alcohol in the presence of an alkaline alcoholysis catalyst, followed by flash distillation of residual alcohol, glycerol and fatty acid esters.
U.S. Pat. No. 2,729,655 teaches that sterols can be recovered from distillate by saponification and acidulation to convert glycerides and sterol esters to free fatty acids and free alcohols (glycerol, sterols respectively). The free fatty acids are esterified with a monohydric lower alcohol. The sterols are crystallized by the addition of a hydrocarbon/water solvent to the mixture.
U.S. Pat. No. 3,153,055 teaches a process for the isolation of sterols and tocopherols from deodorizer distillate by esterification of higher fatty acids into lower monohydric alcohol esters under strongly acidic conditions. The sterols and tocopherols are fractionally extracted from the esterification product with a combination of polar and nonpolar solvents.
U.S. Pat. No. 3,335,154 teaches that the distillate is saponified and acidulated to convert glycerides and sterol esters to free fatty acids and free alcohols (glycerol, sterols respectively). The free fatty acids are esterified with a monohydric lower alcohol and mineral acid catalyst. The sterols are precipitated by the addition of water to the mixture, and the tocopherols are concentrated by removal of the fatty esters by molecular distillation.
U.S. Pat. No. 3,840,570 teaches that sterols can be concentrated from a plant-derived source-by phase separation caused by the addition of a water-alcohol solvent. Sterol esters are saponified with an alkali metal base and free sterols are crystallized from an aprotic solvent.
U.S. Pat. No. 4,148,810 teaches that sterols can be isolated by transesterification of distillate with methanol, catalyzed by alkali metal alcoholates or alkali metal hydroxides. The sterols are isolated from the transesterification mixture by adduct formation with calcium chloride in an aprotic solvent.
U.S. Pat. Nos. 4,374,776 and 4,451,564 teach a method for the concentration of sterols by base-catalyzed transesterification of distillate residues with a lower monohydric alcohol, followed by molecular distillation. The base catalyst is an alkali metal alcoholate or alkali metal hydroxide. The use of alkaline transesterification catalysts in the methods discussed above suffer a major disadvantage in that they require that the mixture be free of all acidic components that would neutralize the alkaline catalyst. This is most unsatisfactory in the case of tocopherols in that they are phenolic compounds and can react with methoxide ion. Other drawbacks of the above processes are that they require multiple reactor systems and processing steps, product purification, relatively low yields, and low through-put.